The present invention relates to an electronic control unit for steering the back wheels of a road vehicle. The electronic control unit is of the type having the following elements: a steering means that, in turn controlled by an emergency steering signal in an emergency, controls the steering angle of the back wheels in emergency-suited fashion in accord with a selected emergency operation concept, i.e., for example, controls the steering angle to zero in delayed fashion or, for example, rigidly maintains the most recently established steering angle; sensors that at least respectively acquire the steering angle, the traveling speed and the degree of steering wheel lock or quantities respectively dependent thereon; and a calculating unit that contains a computer means to which the sensor signals and/or signals derived therefrom are supplied as control signals that outputs the emergency steering signal to the steering means in an emergency dependent on a program-controlled evaluation of the control signals that recognizes emergencies, also see EP-A2-0 243 180 and U.S. Pat. No. 4,687,314. What is thus involved is a control unit also governs emergencies--for example slipping wheels, a road vehicle that has spun out and/or defects in safety-relevant electronic components such as, for example, sensors--more or less well, in that the steering of the back wheels is not controlled as in normal operation but based on a special emergency operation concept. A number of different emergency operation concepts of this type are intrinsically known. The invention was initially in fact developed for an emergency operation concept wherein the steering angle is rigidly retained in an emergency by blocking the steering of the back wheels. It turns out, however, that the invention can also be applied to other emergency operation concepts over and above this.